Acidic zinc electroplating bath

ABSTRACT

AN ACIDIC ZINC ELECTROPLATING BATH YIELDING BRIGHT, DENSE AND NON-EMBRITTLING ZINC DEPOSITS RAPIDLY WITHIN A BROAD RANGE OF CURRENT DENSITY COMPRISES ONE OR MORE ZINC SALTS CORRESPONDING TO 80 TO 200 G./L. OF ZINC, OTHER CONDUCT ING SALTS USUAL LUSTERING AGENTS AND, IN ADDITION, THE REACTION PRODUCT OF EPICHLOROHYDRIN WITH ONE OR MORE MEMBERS OF THE GROUP CONSISTING OF BRANCHED POLYETHYLENE IMINES AND POLYPROPYLENE IMINES, AND, IF DESIRED, LINEAR OR BRANCHED POLYALKYLENE AMINES. REACTION PRODUCTS IN WHICH NOT MORE THAN 90%, PREFERABLY 20 T0 60% OF THE AMINO GROUPS OF THE POLYETHYLENE IMINES, POLYPROPYLENE. IMINES AND POLYALKYLENE AMINES RESPECTIVELY ARE REACTED WITH EPICHLOROHYDRIN ARE PREFERRED.

\Uflit d S ates Pa n us. Cl. 204-55 R 6 Claims ABSTRACT OF THE DISCLOSURE An acidic zinc electroplating bath yielding bright, dense and non-embrittling zinc deposits rapidly within a broad range of current density comprises one or more zinc salts corresponding to 80 to 200 g./l. of zinc, other conducting salts, usual lustering agents and, in addition, the reaction product of epichlorohydrin with one or more members of the .group consisting of branched polyethylene imines and polypropylene imines and, if desired, linear or branched polyalkylene amines. Reaction products in which not more than 90%, preferably 20 to 60% of the amino groups of the polyethylene imines, polypropylene imines and polyalkylene amines respectively are reacted with epichlorohydrin are preferred.

BACKGROUND OF THE INVENTION Generally used zinc electroplating baths for manufacturing galvanized strips, tubes and wires normally contain from 30 to 120 g./l. of zinc and other conducting salts. These baths are used at a temperature of from 40 to 70 C. using a current density of from 20 to 60 amps/ drnfi. Lowering of electrolytic efficiency at such high current densities is prevented by using elevated temperature, high metal concentrations and low pH in the electrolyte. By these measures the desired thickness of the zinc deposits and good current yields are obtained. However, the zinc layers deposited have a more or less rough crystalline structure. The use of elevated current densities should be avoided since the columnar zinc crystals of the deposits i SUMMARY OF THE INVENTION It is an object of the invention to provide a high performance zinc electroplating bath which allows to deposit zinc crystals parallel to the surface of the electroplated article when using higher current densities.

A further object of the invention is to provide compact grained bright, dense and tension-free electroplated zinc deposits which may be rapidly deposited on iron or iron alloys such as strips, tubes and wire. Further objects of the invention may be taken from the following description and claims.

It has been found that bright, dense and non-embrittling zinc deposits may be provided by an acidic zinc electroplating bath comprising in aqueous solution one or more zinc salts corresponding to 30 to 200 g./l. of zinc, other conducting salts, usual lustering agents and, in addition, the reaction product of epichlorohydrin with one or more members of the group consisting of branched polyethylene imines and branched polypropylene imines and, if desired, linear or branched polyalkylene amines.

DESCRIPTION OF THE INVENTION For preparing the reaction products which are contained in the zinc electroplating bath of the invention preferably branched polyethylene imines, branched polypropylene imines and, if desired, alkylene polyamines (polyal kylene amines), such as diethylene triamine, triethylene 3,838,026 Patented Sept. 24, 1974 tetramine, tetraethylene pentamine, hexamethylene tetramine or dimethylaminopropylene amine are reacted with epichlorohydrin. 1 1

Since these reaction products should be soluble in the zinc electroplating bath and should not form resins it is preferred to react not more than about of the free amino groups with epichlorohydrin. Thus the molar ratio between the branched polyethylene imines and/or polypropylene imines and, if present, the polyalkylene amines at one hand and epichlorohydrin at the other hand should be chosen in a way to ensure that not more than 90%, preferably 20 to 60% of the amino groups present are reacted with epichlorohydrin.

The concentration of the reaction products of the branched polyethylene imines and polypropylene imines respectively with epichlorohydrin in the electroplating bath amount to 0.02 to 5.0 g./l., preferably 0.1 to 1.0 g./l. of the bath. The concentration of the reaction products of polyalkylene amines with epichlorohydrin which may be used in addition, if desired, amount to 0.01 to 2.0 g./l., preferably 0.1 to 0.5 g./l. of the bath.

The current density used during electroplating with the bath of the invention may amount to from 10 to amps/dm. at a temperature of from 45 to 65 C. and a pH of from 2.9 to 3.8.

The other components of the aqueous electroplating bath of the invention are known as such. Besides zinc salts, such as zinc sulfate and Zinc chloride, conducting salts, such as aluminum sulfate, and boric acid and lustering agents, such as urea, aromatic sulfonamides and -imides, e.g. toluene sulfonamide or o-sulfobenzoic amide may be used.

The invention is further illustrated by the followin examples.

EXAMPLE I An aqueous zinc electroplating bath is prepared from the following ingredients:

380 g./l. of zinc sulfate 20 g./l. of boric acid 20 g./l of aluminum sulfate 4 g./l. of zinc chloride 0.25 g./l. of urea 0.25 g./l. of toluene sulfonamide 0.5 g./l. of the reaction product of a branched polyethylene imine with epichlorohydrin and 0.2 g./l. of the reaction product of tetraethylene pentamine with epichlorohydrin.

At a bath temperature of 55 C. using a current density of from 10 to 65 amps/dm. at a pH of 3.2 brilliant, well adhering and soft zinc deposits on iron are obtained.

The reaction product of the branched polyethylene imine with epichlorohydrin was obtained by reacting one mole of a polyethylene imine having structural units of the formula 3 EXAMPLE n An aqueous zinc electroplating bath is prepared from the following ingredients:

850 g./l. of zinc sulfate 15 g./l. of boric acid 25 g./l. of aluminum sulfate 3 g./l. of zinc chloride 0.25 g/l. of urea 0.45 g./l. of o-sulfobenzoic amide 0.7 g./l. of the reaction product of polypropylene imine with epichlorohydrin and 0.25 g./l. of the reaction product of triethylene tetramine with epichlorohydrin.

At a bath temperature of 55 C. using a current density of from to 100 amps/dm. at a pH of 3.0 brilliant, soft, well-adhering and non-embrittling zinc deposits on iron are obtained.

The reaction product of polypropylene imine with epichlorohydrin was obtained by reacting one mole of a branched polypropylene imine having a molecular weight of about 2500 with four moles of epichlorohydrin at a temperature of 95 C. within a period of 45 minutes.

The reaction product of triethylene tetramine with epichlorohydrin was obtained by reacting one mole of triethylene tetramine with one mole of epichlorohydrin.

EXAMPLE III An aqueous Zinc electroplating bath is prepared from the following ingredients:

850 g./l. of zinc sulfate g./1. of boric acid g./l. of aluminum sulfate 3 g./l. of zinc chloride 0.25 g/l. of urea 0.45 g./l. of toluene sulfonamide 0.30 g./l. of the reaction product of polyethylene imine with epichlorohydrin and 0.20 g./l. of the reaction product of hexamethylene tetramine with epichlorohydrin.

At a bath temperature of 55 C. using a current density of from 10 to 100 amps/dm. at a pH of 3.2 brilliant, well-adhering soft zinc deposit on iron which were free of tension are obtained.

The reaction product of polyethylene imine with epichlorohydrin was obtained by reacting one mole of a branched polyethylene imine having a molecular weight of about 2000 with six moles of epichlorohydrin at a temperature of 95 C. within a period of minutes. The reaction product of hexamethylene tetramine with epichlorohydrin was obtained by reacting one mole of hexamethylene tetramine with one mole of epichlorohydrin at a temperature of 95 C. within 30 minutes.

What is claimed is:

1. In an acid zinc electroplating bath comprising, in aqueous solution, at least one zinc salt in an amount corresponding to between about g./l. and about 200 g./ l. of zinc, the improvement which consists in said bath additionally containing 0.5 g./l. of a water-soluble polyalkylene imine-epichlorohydrin reaction product produced by reacting one mole of a branched polyethylene imine of molecular weight 2000 with two moles of epichlorohydrin at a temperature of C. for a period of 30 minutes.

2. The acid zinc electroplating bath of Claim 1, further comprising 0.2 g./l. of a polyalkylene amine-epichlorohydrin reaction product obtained by reacting one mole of tetraethylene pentamine with one mole of epichlorohydrin at a temperature of 95 C. for a period of 30 minutes.

3. In an acid Zinc electroplating bath comprising, in aqueous solution, at least one zinc salt in an amount corresponding to between about 80 g./l. and about 200 g./l. of zinc, the improvement which consists in said bath additionally containing 0.7 g./l. of a water-soluble polyalkylene imine-epichlorohydrin reaction product produced by reacting one mole of a branched polypropylene imine of molecular weight 2500 with four moles of epichlorohydrin at a temperature of 95 C. for a period of 45 minutes.

4. The acid zinc electroplating bath of Claim 3, further comprising 0.25 g./l. of a polyalkylene amineepichlorohydrin reaction product produced by reacting one mole of triethylene tetramine with one mole of epichlorohydrin at a temperature of 95 C. for a period of 30 minutes.

5. In an acid zinc electroplating bath comprising in aqueous solution, at least one zinc salt in an amount corresponding to between about 80 g./l. and about 200 g./l. of zinc, the improvement which consists in said bath additionally containing 0.30 g./l. of a water-soluble polyalkylene imine-epichlorohydrin reaction product produced by reacting one mole of a branched polyethylene imine of molecular weight 2000 with six moles of epichlorohydrin at a temperature of 95 C. for a period of 30 minutes.

6. The acid zinc electroplating bath of Claim 5, further comprising 0.20 g./l. of a polyalkylene amine-epichlorohydrin reaction product produced by reacting one 'mole of hexamethylene tetramine with one mole of epichlorohydrin at a temperature of 95 C. for a period of 30 minutes.

References Cited UNITED STATES PATENTS 2,384,300 9/1945 Harford 20455 R 2,451,426 10/1948 Bair et al 204-55 Y 3,227,638 1/1966 Burnson 204-55 Y X FOREIGN PATENTS 1,910,466 9/ 1970 Germany.

GERALD L. KAPLAN, Primary Examiner 

